Giving investiture initially in ruined castle (7)
I believe the answer is:
elastic
'giving' is the definition.
(thesaurus)
'investiture initially in ruined castle' is the wordplay.
'initially' suggests taking the first letters.
'in' indicates putting letters inside.
'ruined' is an anagram indicator.
The first letter of 'investiture' is 'i'.
'castle' with letters rearranged gives 'elastc'.
'i' inserted into 'elastc' is 'ELASTIC'.
(Other definitions for elastic that I've seen before include "Able to give a bit" , "Resilient" , "Stretch material" , "Variable" , "Like a small band" .)